System and method for establishing a d2d communication group

ABSTRACT

Systems and methods are disclosed for establishing a device-to-device (D2D) group amongst a plurality of user equipments (UEs). In one embodiment a target UE transmits, using D2D communication, a request message inviting at least one other UE to be part of a D2D group with the target UE. A neighbour UE receives the request message and transmits a report message indicating that the neighbour UE will be part of the D2D group with the target UE. A base station receives the report message and transmits to the target UE and to the neighbour UE a confirmation message indicating that the neighbour UE is in the D2D group with the target UE.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/949,671, which was filed on Apr. 10, 2018 and entitled “System andMethod for Establishing a D2D Communication Group”, which in turn is acontinuation of U.S. patent application Ser. No. 15/060,018, which wasfiled on Mar. 3, 2016, and is now granted as U.S. Pat. No. 9,967,910,and entitled “System and Method for Establishing a D2D CommunicationGroup”.

Both of the patent applications mentioned immediately above areincorporated herein by reference.

FIELD

The present application relates to establishing a device-to-devicecommunication group amongst user equipment.

BACKGROUND

In a traditional mobile network, all messages between two userequipments (UEs) pass through a base station, even if the two UEscommunicating with each other are in close physical proximity.

Device-to-device (D2D) communication has more recently been introducedto allow for UEs in close proximity to directly communicate with eachother without using the base station.

As the number of UEs in a mobile network increases, there may be morepotential opportunities for D2D communication.

SUMMARY

Systems and methods are disclosed for establishing a D2D group amongst aplurality of UEs.

In one embodiment, there is provided a method that may include a targetUE transmitting, using D2D communication, a request message inviting atleast one other UE to be part of a D2D group with the target UE. Aneighbour UE may receive the request message and transmit a reportmessage indicating that the neighbour UE will be part of the D2D groupwith the target UE. A base station of a network may receive the reportmessage and transmit to the target UE and to the neighbour UE aconfirmation message indicating that the neighbour UE is in the D2Dgroup with the target UE. After receiving the confirmation message, theneighbour UE may communicate with the target UE, using D2Dcommunication, to assist with wireless communication between the targetUE and the base station.

In another embodiment, there is provided a system that may include atarget UE configured to transmit, using D2D communication, a requestmessage inviting at least one other UE to be part of a D2D group withthe target UE. The system may further include neighbour UE configured toreceive the request message and transmit a report message indicatingthat the neighbour UE will be part of the D2D group with the target UE.The system may further include a base station of a network configured toreceive the report message and transmit to the target UE and to theneighbour UE a confirmation message indicating that the neighbour UE isin the D2D group with the target UE. The neighbour UE may be furtherconfigured to: after receiving the confirmation message, communicatewith the target UE, using D2D communication, to assist with wirelesscommunication between the target UE and the base station.

In another embodiment, there is provided a method performed by a UE thatmay include transmitting, using D2D communication, a request messageinviting at least one other UE to be part of a D2D group with the UE.The method may further include receiving a confirmation message from abase station indicating that a neighbour UE is in the D2D group with theUE. The confirmation message may be in response to a report message tothe base station indicating that the neighbour UE will be part of theD2D group with the UE.

In another embodiment, there is provided a UE that may include at leastone antenna. The UE may further include a D2D communication moduleconfigured to instruct the UE to: transmit, using D2D communication, arequest message inviting at least one other UE to be part of a D2D groupwith the UE; and/or receive a confirmation message from a base stationindicating that a neighbour UE is in the D2D group with the UE. Theconfirmation message may be in response to a report message to the basestation indicating that the neighbour UE will be part of the D2D groupwith the UE.

In another embodiment, there is provided a method performed by a UE thatmay include receiving, using D2D communication, a request messageinviting at least one UE to be part of a D2D group with a target UE. Themethod may further include transmitting a report message to a basestation indicating that the UE will be part of the D2D group with thetarget UE. The method may further include receiving a confirmationmessage from the base station indicating that the UE is in the D2D groupwith the target UE.

In another embodiment, there is provided a UE that may include at leastone antenna. The UE may further include a D2D communication moduleconfigured to instruct the UE to: receive, using D2D communication, arequest message inviting at least one UE to be part of a D2D group witha target UE; and/or transmit a report message to a base stationindicating that the UE will be part of the D2D group with the target UE;and/or receive a confirmation message from the base station indicatingthat the UE is in the D2D group with the target UE.

In another embodiment, there is provided a method performed by a basestation of a network. The method may include receiving a report messagefrom a neighbour UE indicating that the neighbour UE will be part of aD2D group with a target UE upon the neighbour UE receiving a requestmessage inviting at least one UE to be part of a D2D group with thetarget UE. The method may further include transmitting to the target UEand to the neighbour UE a confirmation message indicating that theneighbour UE is in the D2D group with the target UE.

In another embodiment, there is provided a system in a network. Thesystem may include a base station. The system may further include a D2Dcommunication module configured to instruct the base station to: receivea report message from a neighbour UE indicating that the neighbour UEwill be part of a D2D group with a target UE upon the neighbour UEreceiving a request message inviting at least one UE to be part of a D2Dgroup with the target UE; and/or transmit to the target UE and to theneighbour UE a confirmation message indicating that the neighbour UE isin the D2D group with the target UE.

Other aspects and features will become apparent to those of ordinaryskill in the art upon review of the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described, by way of example only, with reference tothe accompanying figures wherein:

FIG. 1 is a block diagram of a telecommunications network according toone embodiment;

FIG. 2 is a block diagram of a network serving two UEs according to oneembodiment;

FIG. 3 is a flowchart of operations performed by a base station, targetUE, and neighbour UE according to one embodiment;

FIG. 4 is a flowchart of operations corresponding to FIG. 3, but fromthe perspective of the target UE;

FIG. 5 is a flowchart of operations corresponding to FIG. 3, but fromthe perspective of the neighbour UE;

FIG. 6 is a flowchart of operations corresponding to FIG. 3, but fromthe perspective of the base station;

FIG. 7 is a flowchart of operations performed by a base station, targetUE, and neighbour UE according to another embodiment;

FIG. 8 is a flowchart of operations corresponding to FIG. 7, but fromthe perspective of the target UE;

FIG. 9 is a flowchart of operations corresponding to FIG. 7, but fromthe perspective of the neighbour UE;

FIG. 10 is a flowchart of operations corresponding to FIG. 7, but fromthe perspective of the base station;

FIG. 11 is a flow chart of operations performed by four UEs and a basestation to establish a D2D group according to one embodiment; and

FIG. 12 is a flow chart of operations performed by UEs and a basestation to establish two D2D groups in accordance with one embodiment.

DETAILED DESCRIPTION

For illustrative purposes, specific example embodiments will now beexplained in greater detail below in conjunction with the figures.

FIG. 1 is a block diagram of a telecommunications network 100 accordingto one embodiment. The telecommunications network 100 includes a corenetwork 102 and an access network 106. The access network 106 serves aplurality of UEs 104 a, 104 b, 104 c, 104 d, 104 e, 104 f, 104 g, 104 h,and 104 i. The access network 106 may be an Evolved UniversalTerrestrial Access (E-UTRA) network. As another example, the accessnetwork 106 may be a cloud access network (C-RAN). The access network106 includes a plurality of base stations 108 a, 108 b, and 108 c. Thebase stations 108 a-c each provide a respective wireless coverage area110 a, 110 b, and 110 c. Each of the base stations 108 a-c may beimplemented using a radio transceiver, one or more antennas, andassociated processing circuitry, such as antenna radio frequency (RF)circuitry, analog-to-digital/digital-to-analog converters, etc.

Although not illustrated, the base stations 108 a-c are each connectedto the core network 102, either directly or through one or more centralprocessing hubs, such as servers. The base stations 108 a-c may serve asthe gateway between the wireline and wireless portion of the accessnetwork 106.

Each one of base stations 108 a-c may instead be referred to as a basetransceiver station, a radio base station, a network node, a transmitnode, a transmit point, a Node B, an eNode B, or a remote radio head(RRH), depending upon the implementation.

In operation, the plurality of UEs 104 a-i access the telecommunicationsnetwork 100 using the access network 106 by wirelessly communicatingwith one or more of the base stations 108 a-c.

UEs 104 a-d are in close proximity to each other. Although the UEs 104a-d can each wirelessly communicate with the base station 108 a, theycan also directly communicate with each other using D2D communications116. A D2D communication is a direct communication between UEs that doesnot go through an access network component, such as a base station.Instead, a D2D communication goes through a D2D communication interface.As shown in FIG. 1, D2D communications 116 are directly between the UEs104 a-d and are not routed through the base station 108 a, or any otherpart of the access network 106. D2D communications 116 may also bereferred to as lateral communications. D2D communications use a sidelinkchannel and a sidelink D2D air interface. On the other hand, acommunication between an access network component, such as base station108 a, and a UE, as in communication 114, is called an accesscommunication. An access communication occurs over an access channel,which can be an uplink or downlink channel, and an access communicationuses a radio access communication interface, such as a cellular radioaccess air interface. Access and D2D air interfaces may use differenttransmission formats, such as different waveforms, different multipleaccess schemes, and/or different radio access technologies. Someexamples of radio access technologies that may be used by an access airinterface and/or a D2D air interface are: Long Term Evolution (LTE), LTELicense Assisted Access (LTE-LAA), and WiFi.

By using the D2D communications 116, the UEs 104 a-d may be able toassist with wireless communications between the UEs 104 a-d and the basestation 108 a. As one example, if UE 104 c fails to correctly decode apacket received from the base station 108 a, but if UE 104 d is able toreceive and correctly decode the packet from the base station 108 a,then UE 104 d could directly transmit the decoded packet to UE 104 cusing D2D communications 116. As another example, if UE 104 c moves outof wireless coverage area 110 c, such that UE 104 c can no longerwirelessly communicate with the base station 108 a, then UE 104 b mayforward messages between the UE 104 c and the base station 108 a. Asanother example, UE 104 a and UE 104 c may both receive a signaltransmitted from the base station 108 a that carries a packet meant forUE 104 c. UE 104 a may then transmit to UE 104 c, via D2D communications116, the signal as received by UE 104 a. UE 104 c may then use theinformation received from UE 104 a to help decode the packet from thebase station 108 a. In these examples, capacity and/or coverage may beenhanced through the assistance of UEs 104 a, 104 b, and/or 104 d.

The UEs 104 a-d form a D2D group 120. The access network 106 may assigna D2D group identifier (ID) to the D2D group 120. The D2D group ID mayallow the access network 106 to address the D2D group 120 as a whole anddistinguish the D2D group 120 from other D2D groups. The D2D group IDmay also be used to broadcast information within the D2D group, i.e.address all other UEs within the D2D group 120. The D2D group 120 mayform a logical or virtual device mesh in which the members of the D2Dgroup 120 communicate amongst themselves using D2D communications over aD2D air interface, but the D2D group 120 as a whole acts as a singledistributed virtual transceiver with respect to the access network 106.The D2D group ID may be a group radio network temporary identifier(G-RNTI).

When a particular UE in the D2D group 120 is being assisted or is to beassisted with wireless communication between that UE and the basestation 108 a, then that particular UE is referred to as the target UE.In the examples above, UE 104 c is being assisted and so is the targetUE 104 c. Therefore, target UE 104 c is labelled with a “T” in FIG. 1.The other UEs 104 a, 104 b, and 104 d in the D2D group 120 form acooperation candidate set, which is a set of UEs that may cooperate tohelp the target UE 104 c. The subset of UEs in the cooperation candidateset that actually assist the target UE 104 c form a cooperation activeset. The cooperation active set may be dynamically selected to assistthe target UE 104 c. The UEs in the cooperation active set are referredto as cooperating UEs (CUEs). In D2D group 120, UEs 104 a, 104 b, and104 d form the cooperation candidate set. If UEs 104 a and 104 bactually assist target UE 104 c, then UEs 104 a and 104 b form thecooperation active set and are the CUEs. As UEs 104 a-d move around,some may leave the D2D group 120 and/or other UEs may join the D2D group120. Therefore, the cooperation candidate set may change over time,e.g., the cooperation candidate set may change semi-statically. The D2Dgroup 120 may also be terminated by the network 106, e.g., if thenetwork 106 determines that there is no longer a need or opportunity forthe D2D group 120 to provide assistance in wireless communicationbetween the base station 108 a and members of the D2D group 120.

There may be more than one D2D group. For example, UEs 104 e and 104 fin FIG. 1 form another D2D group 122.

For a D2D group to exist, the D2D group must first be established. D2Dgroup establishment is discussed below.

FIG. 2 is a block diagram of a network 252 serving two UEs 254 a and 254b, according to one embodiment. The network 252 may be the accessnetwork 106 from FIG. 1, and the two UEs 254 a and 254 b may be two ofthe four UEs 104 a-d in FIG. 1, or the UEs 254 a and 254 b may be UEs104 e and 104 f in FIG. 1. However, more generally this need not be thecase, which is why different reference numerals are used in FIG. 2.

The network 252 includes a base station 256 and a managing module 258.The managing module 258 instructs the base station 256 to performactions. The managing module 258 is illustrated as physically separatefrom the base station 256 and coupled to the base station 256 via acommunication link 260. For example, the managing module 258 may be partof a server in the network 252. Alternatively, the managing module 258may be part of the base station 256.

The managing module 258 includes a processor 262, a memory 264, and aD2D communication module 266. The D2D communication module 266 isimplemented by the processor 262 when the processor 262 accesses andexecutes a series of instructions stored in the memory 264, theinstructions defining the actions of the D2D communication module 266.When the instructions are executed, the D2D communication module 266causes the base station 256 to perform the actions described herein sothat the network 252 can establish, coordinate, instruct, and/or controla D2D group. Alternatively, the D2D communication module 266 may beimplemented using dedicated integrated circuity, such as an applicationspecific integrated circuit (ASIC) or a programmed field programmablegate array (FPGA).

The UE 254 a includes a communication subsystem 270 a, two antennas 272a and 274 a, a processor 276 a, and a memory 278 a. The UE 254 a alsoincludes a D2D communication module 280 a. The D2D communication module280 a is implemented by the processor 276 a when the processor 276 aaccesses and executes a series of instructions stored in the memory 278a, the instructions defining the actions of the D2D communication module280 a. When the instructions are executed, the D2D communication module280 a causes the UE 254 a to perform the actions described herein inrelation to establishing and participating in a D2D group.Alternatively, the D2D module 280 a may be implemented by dedicatedintegrated circuity, such as an ASIC or an FPGA.

The communication subsystem 270 a includes processing andtransmit/receive circuitry for sending messages from and receivingmessages at the UE 254 a. Although one communication subsystem 270 a isillustrated, the communication subsystem 270 a may be multiplecommunication subsystems. Antenna 272 a transmits wireless communicationsignals to, and receives wireless communications signals from, the basestation 256. Antenna 274 a transmits D2D communication signals to, andreceives D2D communication signals from, other UEs, including UE 254 b.In some implementations there may not be two separate antennas 272 a and274 a. A single antenna may be used. Alternatively, there may be severalantennas, but not separated into antennas dedicated only to D2Dcommunication and antennas dedicated only to communicating with the basestation 256.

D2D communications may be over Wi-Fi, in which case the antenna 274 amay be a Wi-Fi antenna. Alternatively, the D2D communications may beover Bluetooth™, in which case the antenna 274 a may be a Bluetooth™antenna. The D2D communications may utilize uplink and/or downlinkresources, such as time slots and/or frequencies, which may be scheduledby the network 252. The D2D communications may be over licensed orunlicensed spectrum.

The UE 254 b includes the same components described above with respectto the UE 254 a. That is, UE 254 b includes communication subsystem 270b, antennas 272 b and 274 b, processor 276 b, memory 278 b, and D2Dcommunication module 280 b.

The UE 254 a is designated as a target UE (TUE) and will therefore becalled TUE 254 a. The UE 254 b is a neighbouring UE (NUE) and willtherefore be called NUE 254 b. The NUE 254 b may be able to assist withwireless communications between the base station 256 and TUE 254 a if aD2D group were to be established that included TUE 254 a and NUE 254 b.

UE 254 a may be specifically chosen as the target UE by the network 252.Alternatively, the UE 254 a may itself determine that it wants to be atarget UE and inform the network 252 by sending a message to the basestation 256. Example reasons why UE 254 a may choose or be selected bythe network 252 to be a target UE include: low wireless channel qualitybetween the UE 254 a and the base station 256, many packets to becommunicated between the base station 256 and the UE 254 a, and/or thepresence of a neighbour UE that is a good candidate for helping withcommunications between the base station 256 and the UE 254 a.

UE 254 a need not always stay a target UE. For example, UE 254 a maylose its status as a target UE once there is no longer a need or desirefor assistance with wireless communications between UE 254 a and thebase station 256. UE 254 a may assist another target UE that is aneighbour at a later time. In general, a particular UE may sometimes bea target UE and other times may be a neighbour UE assisting anothertarget UE. Also, sometimes a particular UE may be both a target UEreceiving assistance from one or more neighbour UEs and also a neighbourUE itself assisting another target UE. In the examples below, the UE 254a acts only as a target UE, i.e, TUE 254 a, and the UE 254 b is aneighbour UE to the TUE 254 a, i.e., NUE 254 b.

FIG. 3 is a flowchart of operations performed by the base station 256,TUE 254 a, and NUE 254 b according to one embodiment.

In step 302, the TUE 254 a transmits, using D2D communication, a requestmessage inviting at least one other UE to be part of a D2D group withthe TUE 254 a. In some embodiments, the network 252 controls if and/orwhen step 302 is to happen. For example, prior to step 302 the network252 may transmit a message to the TUE 254 a indicating that the TUE 254a is to perform step 302. The message may help the network 252 tounderstand or track which group it is when a D2D group is established.In some embodiments, the request message transmitted in step 302 is senton a physical sidelink discovery channel (PSDCH). In some embodiments,the request message transmitted in step 302 includes a preamble. Thepreamble may or may not be assigned by the network 252. If the preambleis assigned by the network 252, then the network 252 may transmit amessage to the TUE 254 a providing an indication of which preamble isassigned. The indication may be the preamble itself. The preamble may bea D2D random access preamble. The D2D random access preamble may be acontention-based D2D random access preamble, or the D2D random accesspreamble may be a contention-free D2D random access preamble assigned bythe network 252. For example, prior to step 302, the base station 256may transmit to the TUE 254 a a contention-free D2D random accesspreamble that is to be used or, if the TUE 254 a already has or knowshow to generate D2D random access preambles, then the base station 256may transmit to the TUE 254 a an indication of which D2D random accesspreamble to use. The base station 256 may provide the D2D random accesspreamble, or the indication of the D2D random access preamble, in aradio resource control (RRC) signalling message. The RRC signallingmessage may be sent on a downlink shared channel (DL-SCH). In someembodiments, the D2D random access preamble is a contention-free randomaccess preamble that is based on a Zadoff-Chu (ZC) sequence. Forexample, contention-free D2D random access preambles may be generatedfrom cyclic shifts of a root ZC sequence with a D2D specific root andlength to ensure a particular ZC sequence has zero cross-correlationwith other ZC sequences generated from cyclic shifts of the same root ZCsequence. In some embodiments, the D2D random access preamble includes acyclic prefix to assist in lower complexity frequency-domain processingof the D2D random access preamble at the NUE 254 b.

In some embodiments, a guard period is provided in the request messagein addition to the D2D random access preamble. For example, the guardperiod may be added to the end of the D2D random access preamble. Theguard period may assist in handling timing uncertainty at the NUE 254 b.For example, the NUE 254 b may not know the timing of when the requestmessage in step 302 will be received, and/or when other request messagesfrom other TUEs may be received, and the guard time may assist inhandling interference due to partially overlapping requests messagesfrom different TUEs. UEs such as TUE 254 a and NUE 254 b may not befully synchronized for D2D communications, in which case the guardperiod may accommodate D2D communication timing uncertainty. The D2Dcommunication timing uncertainty may be proportional to the distancebetween UEs. Using a guard period can result in a D2D random accesspreamble length being less than a subframe duration, which may allow D2Drandom access preambles sent by UEs to not interfere with subsequentsubframes that may or may not be used for D2D communication.

In some embodiments, the request message sent from the TUE 254 a in step302 is meant for and specifically identifies NUE 254 b. However, in themethods below the request message sent in step 302 does not identify anyUE in particular, but invites any UE that receives the request messageto be part of a D2D group with the TUE 254 a.

The NUE 254 b receives the request message sent by the TUE 254 a in step302, and the NUE 254 b decides that it will be part of a D2D group withthe TUE 254 a. Therefore, in step 304, the NUE 254 b transmits a reportmessage to the base station 256 indicating that the NUE 254 b will bepart of the D2D group with the TUE 254 a. In some embodiments, the NUE254 b may not always decide to be part of the D2D group with the TUE 254a, in which case the report message is not sent to the base station 256.For example, the NUE 254 b may decide not to join the D2D group with theTUE 254 a if the NUE 254 b does not have a high enough quality D2Dcommunication link with the TUE 254 a and/or if the NUE 254 b does nothave a high enough quality communication link with the base station 256and/or if the NUE 254 b does not have adequate battery power. In otherembodiments, the NUE 254 b may always decide to be part of the D2D groupwith the TUE 254 a, e.g. if the NUE 254 b is a “dummy” UE employed bythe network operator for the purposes of assisting TUEs in the vicinityof the NUE 254 b.

In some embodiments, the report message sent in step 304 is sent on anuplink shared channel (UL-SCH) using an uplink resource granted by thenetwork 252. In this case, the NUE 254 b may need to first request andreceive the uplink resource grant from the network 252. For example, theNUE 254 b may transmit a message to the base station 256 requesting anuplink resource, and the NUE 254 b may receive a response message fromthe base station 256 indicating the uplink resource granted. In otherembodiments, the report message sent in step 304 is sent in a grant-freemanner using dedicated grant-free radio resources pre-assigned by thenetwork 252.

In some embodiments, the report message sent in step 304 includes anindication, such as an index, of the preamble included in the requestmessage from the TUE 254 a. The indication of the preamble may be usedto inform the network 252 that the NUE 254 b is to be part of a D2Dgroup specifically with TUE 254 a, rather than with another TUE that wasassigned another preamble. In some embodiments, the report messageincludes an identifier of the TUE 254 a and/or an identifier of the NUE254 b. The identifier of the NUE 254 b may be a temporary cell radionetwork temporary identifier (TC-RNTI) or a cell radio network temporaryidentifier (C-RNTI) or a core network identifier. Similarly, theidentifier of the TUE 254 a may be a TC-RNTI, a C-RNTI, or a corenetwork identifier. The NUE 254 b may know the identity of the TUE 254 afrom the request message sent by the TUE 254 a.

The base station 256 receives the report message sent in step 304, andin step 306 the base station 256 transmits to the TUE 254 a and to theNUE 254 b a confirmation message indicating that the NUE 254 b is in theD2D group with the TUE 254 a. In some embodiments, the confirmationmessages includes a D2D group ID assigned by the network 252 to the D2Dgroup. The D2D group ID may allow the network 252 to address the D2Dgroup as a whole and distinguish the D2D group from other D2D groups.

In some embodiments, the confirmation message sent in step 304 includesthe indication of the D2D random access preamble sent by the TUE 254 ain the request message. In some embodiments, the confirmation messageincludes an identifier of the TUE 254 a and/or an identifier of the NUE254 b. Including the identifiers may ensure that the TUE 254 a and theNUE 254 b have each other's identities. As above, the identifiers may bea TC-RNTI, a C-RNTI, or a core network identifier. In some embodiments,the confirmation message is sent on a DL-SCH. In some embodiments, theconfirmation message is decoded using a D2D random access radio networktemporary identifier (D2D-RA-RNTI). In some embodiments, theconfirmation message includes a timing correction value used tosynchronize a D2D communication between the TUE 254 a and the NUE 254 b.The timing correction value may have been computed by the NUE 254 b uponreceiving the request message from the TUE 254 a and then sent to thenetwork 252 via the report message in step 304.

In some embodiments, the transmission from the base station 256 in step306 includes other confirmation messages for other UE devices. Forexample, the base station 256 may transmit a signal including both theconfirmation message of step 306 and another confirmation message (notshown) for two other UEs (not shown) confirming that the two other UEsform a different D2D group. If another UE (not shown) also received therequest message from the TUE 254 a in step 302 and transmitted a reportmessage to the base station 256, then the base station 256 may transmita signal including both the confirmation message of step 306 and anotherconfirmation message (not shown) for the TUE 254 a and the other UEconfirming that the other UE is also part of the D2D group with the TUE254 a. A specific example is provided later in relation to FIG. 12.

In some embodiments, after receiving the confirmation message of step306, the TUE 254 a and the NUE 254 b send an acknowledgement to the basestation 256.

In some embodiments, the network 252 broadcasts signalling indicatingwhen the request message in step 302 is to be sent and/or when UEs areto listen for a request message and/or what resources, e.g.time-frequency resources, are to be used to send/receive the requestmessage. For example, in LTE, physical random access channel (PRACH)time-frequency resource information may be broadcast to the UEs via theDL-SCH as part of the System Information Block (“SIB 2”). The SIB 2 maybe indicated in a physical downlink control channel (PDCCH) using asystem information radio network temporary identifier (SI-RNTI). The SIB2 PRACH configuration includes information such as the random accessparameters “PRACH Config index” and “PRACH Frequency Offset”, from whicha UE may deduce the PRACH resource information along with other uplinkparameters. A similar mechanism may be used to signal the D2D PRACHresources for different frequency bands.

In some embodiments, the network 252 may control the amount of powerused by the TUE 254 a to send the request message in step 302. Theamount of power may be increased or decreased by the network 252depending on the number of NUEs that send reporting messages to thenetwork 252. By controlling the amount of power used by the TUE 254 a tosend the request message, interference generated by transmitting therequest message may be controlled, and the power may only be increasedwhen needed. In some embodiments, the TUE 254 a may itself control itsown transmission power when sending the request message in step 302. Oneway in which the power control may be implemented is as follows: arequest message is first sent with a predetermined minimum power level.If not enough NUEs respond, i.e, none or not enough confirmationmessages are received by the TUE 254 a, then the TUE 254 a may send therequest message again at a higher power level. This process may berepeated using a higher power level each time a request message is sentuntil a minimum number of NUEs have joined the D2D group with the TUE254 a.

Once the method of FIG. 3 is complete, the TUE 254 a and the NUE 254 bare part of a D2D group and may communicate with each other directlyusing D2D communications. For example, the NUE 254 b may communicatewith the TUE 254 a, using D2D communication, to assist with wirelesscommunication between the TUE 254 a and the base station 108 a. The TUE254 a may communicate with the NUE 254 b, using D2D communication, to beassisted with wireless communication between the TUE 254 a and the basestation 108 a. The base station 108 a may wirelessly communicate withthe NUE 254 b to assist in wireless communication between the basestation 108 a and the TUE 254 a. The base station 108 a may wirelesslycommunicate with the NUE 254 b to be assisted with wirelesscommunication between the base station 108 a and the TUE 254 a. The basestation 108 a may transmit a message to the NUE 254 b instructing theNUE 254 b to assist with wireless communication between the TUE 254 aand the base station 108 a.

In some embodiments, multiband communication occurs during D2D groupestablishment and operation. Multiband communication is when a UEcommunicates over more than one radio frequency band. For example, TUE254 a may directly communicate with NUE 254 b using D2D communicationsvia a first frequency band, and TUE 254 a may directly communicate withanother NUE (not shown) using D2D communications via a second frequencyband. Multiband operation is discussed in detail in the examplesexplained later in relation to FIG. 11.

In some embodiments, the TUE 254 a, NUE 254 b and network 252 operateaccording to a radio resource control (RRC) protocol, such as a RRCprotocol similar to that deployed as part of the 3GPP LTE-A airinterface. In such RRC protocol, a UE may be in one of two modes:RRC_Connected or RRC_Idle, depending upon whether the UE is connected tothe network 252. A new third mode may now be defined: “RRC_Cooperating”mode, which is a mode independent of RRC_Connected and RRC Idle. When aUE is in RRC_Cooperating mode, it means that the UE is in a D2Dcooperating mode, that is, the UE is configured to use D2Dcommunications to directly communicate with one or more other UEs, e.g.,to assist or be assisted with wireless communication between the UEs anda base station. At the start of the method in FIG. 3, the TUE 254 a willtypically be in RRC_Connected mode, and the NUE 254 b may be in eitherRRC_Connected mode or RRC_Idle mode. By the end of the method in FIG. 3,both the TUE 254 a and the NUE 254 b may be designated by the network252 as being in RRC_Cooperating mode. Even if the TUE 254 a and/or theNUE 254 b subsequently move between RRC_Connected mode and RRC_Idlemode, the TUE 254 a and the NUE 254 b will still always remain inRRC_Cooperating mode as long as the TUE 254 a and the NUE 254 b arecooperating in a D2D group. The network 252 may track which mode the TUE254 a and the NUE 254 b are in during operation, including designatingthe TUE 254 a and the NUE 254 b as being in RRC_Cooperating mode as partof, or at the end of, step 306. When the NUE 254 b is in RRC_Cooperatingmode, it may be referred to as a CUE if it is assisting or to assist theTUE 254 a.

At some point in time in the future after the method of FIG. 3 iscomplete, the NUE 254 b and/or the TUE 254 a will transition out ofRRC_Cooperating mode. For example, the NUE 254 b and/or the TUE 254 amay themselves decide to transition out of RRC_Cooperating mode due to achange in their circumstance that no longer makes them a good candidatefor D2D communication, e.g., low battery power, a low quality or brokenD2D communication link, etc. The network 252 may also instruct NUE 254 band/or TUE 254 a to transition out of RRC_Cooperating mode, e.g., if thenetwork 252 decides to terminate or modify the D2D group. When aparticular UE transitions out of RRC_Cooperating mode, it may still bein RRC_Connected or RRC_Idle mode.

FIG. 4 is a flowchart of operations corresponding to FIG. 3, but fromthe perspective of the TUE 254 a. In step 322, the TUE 254 a transmits,using D2D communication, the request message inviting at least one otherUE to be part of a D2D group with the TUE 254 a. In step 324, the TUE254 a receives the confirmation message indicating that the NUE 254 b isin the D2D group with the TUE 254 a.

FIG. 5 is a flowchart of operations corresponding to FIG. 3, but fromthe perspective of the NUE 254 b. In step 342, the NUE 254 b receives,using D2D communication, the request message inviting at least one UE tobe part of a D2D group with the TUE 254 a. In step 344, the NUE 254 btransmits the report message indicating that the NUE 254 b will be partof the D2D group with the TUE 254 a. In step 346, the NUE 254 b receivesthe confirmation message indicating that the NUE 254 b is in the D2Dgroup with the TUE 254 a.

FIG. 6 is a flowchart of operations corresponding to FIG. 3, but fromthe perspective of the base station 256. In step 362, the base stationreceives the report message indicating that the NUE 254 b will be partof a D2D group with the TUE 254 a. In step 364, the base station 256transmits to the TUE 254 a and to the NUE 254 b the confirmation messageindicating that the NUE 254 b is in the D2D group with the TUE 254 a.

The variations and possible configurations of the request, report, andconfirmation messages that were described above in relation to FIG. 3also apply to FIGS. 4 to 6.

A more specific example will now be described in relation to FIGS. 7 to10. The example described in relation to FIGS. 7 to 10 implements aprotocol reminiscent of the random access procedure used in LTE, butdifferent in that the protocol described in relation to FIGS. 7 to 10 isadapted for the alternative purpose of network-assisted UE discovery andestablishment of a D2D communication group. In addition to RRC_Connectedmode and RRC_Idle mode, a new RRC_Cooperating mode is provided.

FIG. 7 is a flowchart of operations performed by the base station 256,the TUE 254 a and the NUE 254 b, according to one embodiment. In thisexample, the TUE 254 a is in RRC_Connected mode and the NUE 254 b may bein either an RRC_Connected mode or RRC_Idle mode.

In step 402, the base station 256 sends an RRC signalling message on aDL-SCH to the TUE 254 a. The RRC signalling message includes a D2Drandom access preamble. Alternatively, the TUE 254 a may already have orknow how to generate D2D random access preambles, and the RRC signallingmessage instead includes an indication of which D2D random accesspreamble to use. The D2D random access preamble is a contention-freerandom access preamble that is based on a ZC sequence.

In step 404, the TUE 254 a transmits a D2D Group Invite message usingD2D communications on a PSDCH. The D2D Group Invite message is therequest message inviting at least one other UE to be part of a D2D groupwith the target UE 254 a. The D2D Group Invite message includes the D2Drandom access preamble.

The D2D Group Invite message is received by the NUE 254 b. The NUE 254 bdecides that it will be part of the D2D group, but to inform the network252 of this, the NUE 254 b needs an uplink resource to transmit amessage to the network 252. An uplink resource needs to be requested andgranted because in this example the NUE 254 b does not have grant-freetransmission resources. Therefore, in step 406, the NUE 254 b sends aRandom Access Request message to the base station 256 on a PRACH. If theNUE 254 b is in RRC_Idle mode, then the Random Access Request messagesent in step 406 includes a contention-based random access preamble.Otherwise, if the NUE 254 b is in an RRC_Connected mode, then the RandomAccess Request message sent in step 406 includes a contention-freerandom access preamble that was previously assigned by the network 252.

In step 408, the base station 256 transmits a Random Access Response(RAR) message to the NUE 254 b on the DL-SCH. The RAR message sent instep 408 includes:

-   (1) An index indicating the random access preamble sent in step 406    so that the NUE 254 b can confirm the RAR message is indeed for the    NUE 254 b.-   (2) A timing correction value calculated by the base station 256 for    compensating for round-trip-time (RTT) to provide synchronization    between the NUE 254 b and the base station 256.-   (3) A scheduling grant indicating an uplink resource granted to the    NUE 254 b.

If the NUE 254 b is in RRC_Idle mode, the RAR message further includes aTC-RNTI, which is the temporary ID assigned to the NUE 254 b. The RARmessage sent in step 408 is indicated on a PDCCH using a random accessradio network temporary identifier (RA-RNTI), which is a reservedidentifier that the NUE 254 b uses to decode the RAR message.

If the NUE 254 b is in RRC_Connected mode, then a TC-RNTI does not haveto be included in the RAR message, as the NUE 254 b already has aC-RNTI. The C-RNTI is used by the NUE 254 b to decode the RAR message.

The RAR message sent in step 408 may be part of a single transmission bythe base station 256 that also includes RAR messages for other UEs.

In step 410, the NUE 254 b transmits to the base station 256 a D2D GroupReady Report message on the UL-SCH using the uplink resource indicatedin the RAR message sent at step 408. The D2D Group Ready Report messageis the report message indicating that the NUE 254 b will be part of theD2D group with the TUE 254 a. The D2D Group Ready Report messageincludes:

-   (1) An index indicating the D2D random access preamble that was    present in the D2D Group Invite message sent from the TUE 254 a at    step 404. This informs the network 252 that the NUE 254 b is to be    part of a D2D group specifically with TUE 254 a. In general, there    may be multiple TUEs, and the NUE 254 b may receive different D2D    Group Invite messages from different TUEs. By having the NUE 254 b    provide an indication of the D2D random access preamble that was    present in the D2D Group Invite message received and acted upon by    the NUE 254 b, the network 252 will know that the NUE 254 b is to be    part of a D2D group specifically with the TUE associated with that    D2D random access preamble, i.e., TUE 254 a. Note that the network    252 knows which TUE is associated with which D2D random access    preamble, as the D2D random access preamble was assigned by the    network 252, e.g., as in message 402 for TUE 254 a.-   (2) The identifier being used to identify the NUE 254 b. The C-RNTI    of the NUE 254 b is sent if the NUE 254 b is in RRC_Connected mode,    and otherwise the TC-RNTI or the core network identifier of the NUE    254 b is sent if the NUE 254 b is in RRC_Idle mode. Including the    identifier of the NUE 254 b in the D2D Group Ready Repot message    allows the network 252 to identify the sender of the D2D Group Ready    Report message. This identifier may be included as part of a medium    access control (MAC) control element on the UL-SCH.

The NUE 254 b may provide NUE-specific scrambling of the D2D Group ReadyReport message sent in step 410. The scrambling is performed eitherusing the TC-RNTI if the NUE 254 b is in RRC_Idle mode, or using theC-RNTI if the NUE 254 b is in RRC_Connected mode.

Based on the information in the D2D Group Ready Report message, thenetwork 252 determines that NUE 254 b is to be in the D2D group with TUE254 a, and so in step 412 the base station 256 sends a D2D GroupConfirmation message to both NUE 254 b and TUE 254 a on the DL-SCH. TheD2D Group Confirmation message is the confirmation message indicatingthat the NUE 254 b is in the D2D group with the TUE 254 a. The D2D GroupConfirmation message may be called a D2D RAR message. The D2D GroupConfirmation message includes:

-   (1) An index indicating the D2D random access preamble used by TUE    254 a, i.e., an index indicating the D2D random access preamble that    was present in the D2D Group Invite message sent by the TUE 254 a at    step 404.-   (2) The identifier assigned to the TUE 254 a, such as the C-RNTI of    the TUE 254 a. This is so that the NUE 254 b knows the identity of    the TUE 254 a.-   (3) The identifier assigned to the NUE 254 b, such as the C-RNTI of    the NUE 254 b if the NUE 254 b is in RRC_Connected mode or a core    network identifier of the NUE 254 b if the NUE 254 b is in RRC_Idle    mode. This is so that the TUE 254 a knows the identity of the NUE    254 b.-   (4) A D2D group ID assigned by the network 252 to the D2D group. The    D2D group ID may be a G-RNTI.

The D2D Group Confirmation message optionally additionally includes atiming correction value for the TUE 254 a for synchronizing a D2Dcommunication between the TUE 254 a and the NUE 254 b. If the timingcorrection value is included in the D2D Group Confirmation message, thenthe timing correction value first must be obtained by the network 252,e.g., as follows: the timing correction value is computed by the NUE 254b and forwarded to the network 252 as part of the D2D Group Ready Reportmessage sent in step 410.

The D2D Group Confirmation message sent in step 412 is a random accessresponse message that is scrambled and decoded by the TUE 254 a and theNUE 254 b using a D2D specific RA-RNTI. The D2D Group Confirmationmessage may be part of a single transmission by the base station 256that also includes D2D Group Confirmation messages for other UEs, suchas other TUEs and associated NUEs that are in the coverage area of thebase station 256 and that form other D2D groups.

In steps 414 and 416 the NUE 254 b and the TUE 254 a respectively sendan acknowledgement to the base station 256. The receipt of theseacknowledgements confirms for the network 252 that NUE 254 b is in a D2Dgroup with TUE 254 a having the assigned D2D group ID, and that NUE 254b and TUE 254 a are in a D2D cooperating mode.

Steps 414 and 416 are optional. If steps 414 and 416 are omitted thenthe network 252 does not wait for an acknowledgement after sending theD2D Group Confirmation message at step 412. After sending the D2D GroupConfirmation message, the network 252 records that NUE 254 b and TUE 254a are in a D2D cooperating mode.

At the end of step 412, or at the end of steps 414 and 416 if included,the network 252 records that the NUE 254 b and TUE 254 a are both inRRC_Cooperating mode.

At the end of the method of FIG. 7, the NUE 254 b and the TUE 254 a arein an RRC_Cooperating mode. However, the NUE 254 b and/or the TUE 254 amay transition out of RRC_Cooperating mode at a later time, either bychoice or because they are instructed to by the network 252. As oneexample, if the battery level of the NUE 254 b drops below a particularthreshold, or the D2D communication link between the NUE 254 b and theTUE 254 a breaks or degrades to below a particular threshold, then theNUE 254 b may inform the network 252 and transition out ofRRC_Cooperating mode. As another example, if the network 252 determinesthat there is no longer a need for assistance with wirelesscommunication between the base station 256 and the TUE 254 a, then thenetwork 252 may terminate the D2D group by instructing all UEs in theD2D group, including TUE 254 a and NUE 254 b, to transition out ofRRC_Cooperating mode. As another example, if the network 252 determinesthat NUE 254 b is no longer suitable to assist in wireless communicationbetween the base station 256 and the TUE 256 a, then the network 252 mayinstruct the NUE 254 b to transition out of RRC_Cooperating mode,without necessarily terminating the D2D group.

FIG. 8 is a flowchart of operations corresponding to FIG. 7, but fromthe perspective of the TUE 254 a, and illustrating additional operationsperformed by the TUE 254 a. In step 432, the TUE 254 a receives the RRCsignalling message on the DL-SCH that includes or indicates the D2Drandom access preamble. In step 434, the TUE 254 a transmits the D2DGroup Invite message, including the D2D random access preamble, usingD2D communications on the PSDCH. In step 436, the TUE 254 a starts atimer. The TUE 254 a now waits for the D2D Group Confirmation message.If the timer expires then the TUE 254 a concludes that the D2D GroupInvite message was not received by and/or not acted upon by another UE,and so step 434 is repeated, as shown at 438. In this example the D2DGroup Confirmation message is received, as shown at 440, and so in step442 the TUE 254 a sends an acknowledgement to the base station 256, andthen at step 444 the TUE 254 a adds the NUE 254 b to the cooperationcandidate set of the D2D group. The method of FIG. 8 may be repeated totry to further enlarge the D2D group with other neighbour UEs, e.g., ifmore neighbouring UEs are desired or required to have an effective D2Dcooperation group.

FIG. 9 is a flowchart of operations corresponding to FIG. 7, but fromthe perspective of the NUE 254 b, and illustrating additional operationsperformed by the NUE 254 b. In step 454, the NUE 254 b monitors thePSDCH for D2D Group Invite messages. In step 456, the D2D Group Invitemessage sent from TUE 254 a is received by the NUE 254 b. In step 458,the NUE 254 b transmits the Random Access Request message to the basestation 256 on the PRACH to request an uplink resource. If the NUE 254 bis in RRC_Idle mode, then the Random Access Request message includes acontention-based random access preamble. Otherwise, if the NUE 254 b isin an RRC_Connected mode, then the Random Access Request messageincludes a contention-free random access preamble. In step 460, the NUE254 b waits for the RAR Message from the base station 256 on the DL-SCH.If the RAR message is not received, then the NUE 254 b proceeds back tostep 454. Otherwise, when the RAR message is received, in step 462 theNUE 254 b transmits the D2D Group Ready Report message to the basestation 256 on the UL-SCH. The NUE 254 b now starts a timer in step 463and waits for the expected D2D Group Confirmation message from the basestation 256. If the timer expires then the NUE 254 b concludes that aD2D group is not being formed with the NUE 254 b, and so the NUE 254 bproceeds back to step 454, as shown at 464. If a D2D Group Confirmationmessage is received, then the NUE 254 b confirms that the D2D GroupConfirmation message is the expected and correct one by checking thatthe NUE 254 b identifier in the D2D Group Confirmation messages matchesthat of the NUE 254 b, which was sent to the base station 256 in step462. If the D2D Group Confirmation message is not the correct one, thenthe NUE 254 b continues to monitor for D2D Group Confirmation messagesuntil the timer expires, as shown at 466. In this example, the correctD2D Group Confirmation message is received, as shown at 468, and so instep 470 the NUE 254 b sends an acknowledgement to the base station 256,and then at step 472 the NUE 254 b enters into a D2D cooperating modewith the TUE 254 a, i.e., the NUE 254 b enters into RRC_Cooperatingmode.

FIG. 10 is a flowchart of operations corresponding to FIG. 7, but fromthe perspective of the base station 256, and illustrating additionaloperations performed by the base station. In step 484, the base station256 sends the RRC signalling message, including or indicating the D2Drandom access preamble, on the DL-SCH to the TUE 254 a. In step 486, thebase station 256 receives the Random Access Request message from the NUE254 b. The Random Access Request message requests an uplink resource. Instep 488, the base station 256 sends the RAR message to the NUE 254 b.The RAR message grants the uplink resource. In step 490, the basestation 256 receives the D2D Group Ready Report message from the NUE 254b. In step 492, the base station 256 transmits the D2D GroupConfirmation message to both the TUE 254 a and the NUE 254 b. In step494, the base station 256 waits for acknowledgements from both the TUE254 a and the NUE 254 b. If the acknowledgements are not received, thenthe base station 256 concludes that the NUE 254 b will not be part ofthe D2D group, and the base station 256 goes back to waiting for amessage, as shown at 496. Otherwise, if the acknowledgements arereceived, then at step 498 the base station adds the NUE 254 b to thecooperation candidate set for the TUE 254 a.

In the embodiments described above in relation to FIGS. 1 to 10, a D2Dgroup is not established based on the physical proximity of UEs, butinstead based on radio frequency (RF) proximity, and specificallywhether the D2D communication link between a target UE and a neighbourUE is adequate. For example, if the D2D communication link between atarget UE and a neighbour UE is not robust enough for the neighbour UEto receive the request message from the target UE, then the neighbour UEand the target UE will not be part of a D2D group. Neighbour discoverytherefore leverages RF proximity, which may be more accurate thanphysical proximity, as just because two UEs are physically close to eachother, and just because the network may realize this, it does not meanthat there is a good D2D communication link between the two UE devices,e.g., the two UE devices may be on either side of a wall that impedesthe D2D communication link. Also, by using RF proximity instead ofphysical proximity, the UEs may not need to report their physicalpositions to the network, which may save battery power and reduce uplinktraffic. Also, by using RF proximity instead of physical proximity, itmay not be necessary to rely upon Global Positioning System (GPS)signals for D2D group formation or operation, which may result in moresituations in which a D2D group is formed and operates in an indoorenvironment.

The embodiments described above in relation to FIGS. 1 to 10 areindependent of the spectrum bands over which the UEs and base stationcommunicate. Therefore, D2D groups may be formed and operate even whenthe UEs support multiband communication and communicate with each otherover different frequency bands. For example, with reference to FIG. 1,the D2D group 120 includes UEs 104 a-d. A particular UE in the D2D group120, e.g. target UE 104 c, may communicate with the base station 108 aover a frequency band that is different from the frequency bands used byUEs 104 a, 104 b, and 104 d to communicate with base station 108 a. Thetarget UE 104 c may also directly communicate with each of UEs 104 a,104 b, and 104 d using D2D communications, but using a differentfrequency band for each UE. For example, the UE 104 c may directlycommunicate with UE 104 a using D2D communications via a first PSDCH ona first frequency band, and the UE 104 c may directly communicate withUEs 104 b and 104 d using D2D communications via a second PSDCH on asecond frequency band. In multiband operation, UE cooperation mayexploit carrier aggregation by having the target UE 104 c communicatewith UEs 104 a, 104 b, and 104 d using different frequency bands.

FIG. 11 is a flow chart of operations performed by UEs 104 a-d and basestation 108 a to establish D2D group 120, according to one embodiment,in the situation in which UE 104 c is a target UE that communicates withUE 104 a using D2D communications via a first frequency band, and thatcommunicates with UEs 104 b and 104 d using D2D communications via asecond frequency band. In step 502, UE 104 c transmits, using D2Dcommunication on the first frequency band, a first request messageinviting at least one other UE to be part of a D2D group with UE 104 c.At step 504, UE 104 c transmits, using D2D communication on the secondfrequency band, a second request message inviting at least one other UEto be part of a D2D group with UE 104 c. Steps 502 and 504 may occursimultaneously. The UE 104 a receives the first request message, and theUE 104 a decides that it will be part of a D2D group with UE 104 c.Therefore, in step 506 the UE 104 a transmits a report message to thebase station 108 a indicating that the UE 104 a will be part of the D2Dgroup with the UE 104 c. The UE 104 b receives the second requestmessage, and the UE 104 b decides that it will be part of a D2D groupwith UE 104 c. Therefore, in step 508 the UE 104 b transmits a reportmessage to the base station 108 a indicating that UE 104 b will be partof the D2D group with the UE 104 c. The UE 104 d also receives thesecond request message, and the UE 104 d decides that it will be part ofa D2D group with UE 104 c. Therefore, in step 510 the UE 104 d transmitsa report message to the base station 108 a indicating that UE 104 d willbe part of the D2D group with UE 104 c. Steps 506, 508, and 510 mayoccur simultaneously. The base station 108 a receives the report messagefrom UE 104 a and in step 512 transmits to UE 104 a and UE 104 c aconfirmation message indicating that UE 104 a is in the D2D group 120with UE 104 c. The base station 108 a receives the report message fromUE 104 b and in step 514 transmits to UE 104 b and UE 104 c aconfirmation message indicating that UE 104 b is in the D2D group 120with UE 104 c. The base station 108 a receives the report message fromUE 104 d and in step 516 transmits to UE 104 c and UE 104 d aconfirmation message indicating that UE 104 d is in the D2D group 120with UE 104 c. Some or all of the messages sent in steps 508 to 516 maybe sent over different frequency bands if the UEs 104 a-d use differentfrequency bands in their communications with the base station 108 a. Ifthe base stations 104 a-d all use the same frequency band to communicatewith the base station 108 a, then the confirmation messages sent insteps 512, 514, and 516 may all be sent by the base station 108 a in asingle signal transmission, e.g., in a DL-SCH.

After D2D group 120 is formed, UE 104 c directly communicates with UE104 a using D2D communications via the first frequency band, and UE 104c directly communicate with UEs 104 b and 104 d using D2D communicationsvia the second frequency band.

The variations and possible configurations of the request, report, andconfirmation messages that were described above in relation to FIG. 3also apply to FIG. 11.

In multiband operation, some of the frequency bands may be licensedfrequency bands, and other of the frequency bands may be unlicensedfrequency bands. The network 106 may broadcast signalling indicatingwhen request messages are to be sent on each frequency band and/or whenUEs 104 a-d are to listen for a request message on each frequency bandand/or what frequency resources are to be used to send/receive requestmessages on each frequency band. For example, the network 106 mayindicate what resources are to be used by the UEs 104 a-d for sidelinkdiscovery purposes on a PSDCH.

A single transmission from a UE or a base station may serve multiple UEson the same frequency band. For example, FIG. 12 is a flow chart ofoperations performed by UEs 104 a-f and base station 108 a to establishD2D groups 120 and 122, in accordance with one embodiment, in thesituation in which UEs 104 c and 104 f are each a target UE, and in thesituation in which all communications occur on the same frequency band.In step 532, UE 104 c transmits, using D2D communication, a requestmessage inviting at least one other UE to be part of D2D group 120 withUE 104 c. In step 534, UE 104 f transmits, using D2D communication, arequest message inviting at least one other UE to be part of D2D group122 with UE 104 f. Steps 532 and 534 may occur simultaneously. Each oneof the UEs 104 a, 104 b, and 104 d receives the request message from UE104 c and decides that it will join the D2D group 120 with UE 104 c. TheUE 104 e receives the request message from UE 104 f, and the UE 104 edecides that it will join the D2D group 122 with UE 104 f. Each of UEs104 a, 104 b, and 104 d send their own respective report message to thebase station 108 a indicating that they will be part of the D2D group120 with UE 104 c, and UE 104 e also sends its own report message to thebase station 108 a indicating that UE 104 e will be part of D2D group122 with UE 104 f. In this embodiment, all report messages sent from UEs104 a, 104 b, 104 d, and 104 e are transmitted in the same uplinktransmission on a respective uplink resource granted by the base station108, e.g., via an UL-SCH. This is shown at step 536. The base station108 a sends a confirmation message to each of UEs 104 a-d indicatingthat they are in D2D group 120, and the base station 108 a also sends aconfirmation to each of UEs 104 e-f indicating that they are in D2Dgroup 122. In this embodiment, all confirmation messages sent by thebase station 108 a are transmitted in the same downlink transmission, asshown at step 538. In this way, the base station 108 a may receivemultiple report messages from different UEs in a single uplink signaltransmission and may send multiple confirmation messages for differentUEs in a single downlink signal transmission. Optionally, the basestation may indicate to each of UEs 104 a, 104 b, and 104 d what otherUEs are in D2D group 120.

A possible benefit of some embodiments includes centralized networkcontrol to coordinate the D2D discovery and D2D group formation processand thereby possibly result in more efficient utilization of resourcesand less overhead. For example, the network may decide when a D2D groupis to be formed and allocate resources to the appropriate UEs, asneeded, for sending and receiving D2D group invite messages. This may bemore efficient compared to having UEs continually send and monitor forD2D group invite messages at all times, which would affect batteryconsumption and may pose security risks due to possibly having a fullyopen control channel. Another possible benefit of having the networkcontrol the resources for the D2D discovery process is that collisionprobability may be reduced, as the network may control when D2D groupinvite messages are sent. Another possible benefit of network control isthat the network may control which UEs in a D2D group are to form acooperation active set to assist a target UE. The network maydynamically adjust the cooperation active set according to prevailingchannel and interference conditions. Security risks may also bemitigated in some embodiments because, in such embodiments, only UEsassigned the proper D2D Group ID by the network have access to theinformation broadcast by the network for the target UE. Therefore, thenumber of UEs who have access to the target UE's information is limitedonly to the D2D group.

Although the present invention has been described with reference tospecific features and embodiments thereof, various modifications andcombinations can be made thereto without departing from the invention.The description and drawings are, accordingly, to be regarded simply asan illustration of some embodiments of the invention as defined by theappended claims, and are contemplated to cover any and allmodifications, variations, combinations or equivalents that fall withinthe scope of the present invention. Therefore, although the presentinvention and its advantages have been described in detail, variouschanges, substitutions and alterations can be made herein withoutdeparting from the invention as defined by the appended claims.Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

Moreover, any module, component, or device exemplified herein thatexecutes instructions may include or otherwise have access to anon-transitory computer/processor readable storage medium or media forstorage of information, such as computer/processor readableinstructions, data structures, program modules, and/or other data. Anon-exhaustive list of examples of non-transitory computer/processorreadable storage media includes magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, optical diskssuch as compact disc read-only memory (CD-ROM), digital video discs ordigital versatile disc (DVDs), Blu-ray Disc™, or other optical storage,volatile and non-volatile, removable and non-removable media implementedin any method or technology, random-access memory (RAM), read-onlymemory (ROM), electrically erasable programmable read-only memory(EEPROM), flash memory or other memory technology. Any suchnon-transitory computer/processor storage media may be part of a deviceor accessible or connectable thereto. Any application or module hereindescribed may be implemented using computer/processorreadable/executable instructions that may be stored or otherwise held bysuch non-transitory computer/processor readable storage media.

1. A method performed by a target user equipment (UE), the methodcomprising: transmitting, using device-to-device (D2D) communication, afirst request message to a first neighbour UE, the first request messagebeing sent on a first frequency band, and the first request messageinviting the first neighbour UE to be part of a D2D group with thetarget UE; transmitting, using D2D communication, a second requestmessage to a second neighbour UE, the second request message being senton a second frequency band different from the first frequency band, andthe second request message inviting the second neighbour UE to be partof the D2D group with the target UE; receiving at least one confirmationmessage from the base station, the at least one confirmation messageindicating that the first neighbour UE and the second neighbour UE areboth in the D2D group with the target UE; communicating with the firstneighbour UE on the first frequency band using D2D communication, andcommunicating with the second neighbour UE on the second frequency bandusing D2D communication.
 2. The method of claim 1, wherein the firstfrequency band is a licensed frequency band and the second frequencyband is an unlicensed frequency band.
 3. The method of claim 1, furthercomprising receiving signaling from a network, the signaling indicating:when the first request message is to be sent on the first frequency bandand/or when the second request message is to be sent on the secondfrequency band.
 4. The method of claim 1, further comprising receivingsignaling from a network, the signaling indicating: a first frequencyresource on which the first request message is to be sent on the firstfrequency band and/or a second frequency resource on which the secondrequest message is to be sent on the second frequency band.
 5. Themethod of claim 1, further comprising: prior to transmitting the firstrequest message and the second request message, receiving a messageindicating that the target UE is to transmit the first request messageand the second request message.
 6. The method of claim 5, wherein themessage indicating that the target UE is to transmit the first requestmessage and the second request message comprises: an indication of apreamble assigned by a network and/or the preamble assigned by thenetwork.
 7. The method of claim 6, wherein the first request messageincludes the preamble.
 8. The method of claim 7, wherein the at leastone confirmation message includes an indication of the preamble.
 9. Themethod of claim 7, wherein the preamble is a contention-free randomaccess preamble that is based on a Zadoff-Chu (ZC) sequence.
 10. Themethod of claim 1, wherein the confirmation message includes a D2D groupID assigned by a network to the D2D group.
 11. A target user equipment(UE) comprising: at least one antenna; a processor configured toinstruct the target UE to: transmit, using D2D communication, a firstrequest message to a first neighbour UE, the first request message beingsent on a first frequency band, and the first request message invitingthe first neighbour UE to be part of a D2D group with the target UE;transmit, using D2D communication, a second request message to a secondneighbour UE, the second request message being sent on a secondfrequency band different from the first frequency band, and the secondrequest message inviting the second neighbour UE to be part of the D2Dgroup with the target UE; receive at least one confirmation message fromthe base station, the at least one confirmation message indicating thatthe first neighbour UE and the second neighbour UE are both in the D2Dgroup with the target UE; communicate with the first neighbour UE on thefirst frequency band using D2D communication, and communicate with thesecond neighbour UE on the second frequency band using D2Dcommunication.
 12. The target UE of claim 11, wherein the firstfrequency band is a licensed frequency band and the second frequencyband is an unlicensed frequency band.
 13. The target UE of claim 11,wherein the at least one antenna is configured to receive signaling froma network, the signaling indicating: when the first request message isto be sent on the first frequency band and/or when the second requestmessage is to be sent on the second frequency band.
 14. The target UE ofclaim 11, wherein the at least one antenna is configured to receivesignaling from a network, the signaling indicating: a first frequencyresource on which the first request message is to be sent on the firstfrequency band and/or a second frequency resource on which the secondrequest message is to be sent on the second frequency band.
 15. Thetarget UE of claim 11, wherein prior to transmitting the first requestmessage and the second request message, the at least one antenna isconfigured to receive a message indicating that the target UE is totransmit the first request message and the second request message. 16.The target UE of claim 15, wherein the message indicating that thetarget UE is to transmit the first request message and the secondrequest message comprises: an indication of a preamble assigned by anetwork and/or the preamble assigned by the network.
 17. The target UEof claim 16, wherein the first request message includes the preamble.18. The target UE of claim 17, wherein the at least one confirmationmessage includes an indication of the preamble.
 19. The target UE ofclaim 17, wherein the preamble is a contention-free random accesspreamble that is based on a Zadoff-Chu (ZC) sequence.
 20. The target UEof claim 11, wherein the confirmation message includes a D2D group IDassigned by a network to the D2D group.